Landlord entering, etc. without permission

[BrooklynRenter]

I would be very grateful for advice/tips:

We officially moved out of our last apartment the last day of July, so we paid rent through the end of the day July 31st. We moved most of our stuff out July 24th, but informed the landlords on this day that we would be returning to clean up and get the rest of our things. When we returned on the 31st, the door to our apartment was wide open, some of our things had been moved or plugged in, and there were items belonging to the landlords in our bathroom, kitchen, and living room. They had obviously been using our apartment.

We did not comment at the time, but now another dispute has come up (see my other post). Can we do anything about this?